Process for producing alkyl esters of omega-cyano-acids

ABSTRACT

ALKYL W-CYANO-VALERATES AND 5-CYANO-PENTEN-4-OATES ARE PREPARED BY A PROCESS WHICH COMPRISES HEATING A MIXTURE OF ACRYLONITRILE AND AN ALKYL ACRYLATE UNDER HYDROGEN PRESSURE IN THE PRESENCE OF A RUTHENIUM COMPOUND AS CATALYST.

United States Patent Int. Cl. C07c 121/02 U.S. c1. 260--465.4 4 Claims ABSTRACT OF THE DISCLOSURE Alkyl w-cyano-valerates and S-cyano-penten-4-oates are prepared by a process which comprises heating a mixture of acrylonitrile and an alkyl acrylate under hydrogen pressure in the presence of a ruthenium compound as catalyst.

The present invention relates to the production of alkyl esters of w-cyanovaleric acid and of cis and trans 5-cyano penten-4-oic acids. The latter are new compounds.

Various processes for converting acrylonitrile into dimerisation or hydrodimerisation products have been proposed. Whether linear or branched products are obtained depends on the process used. Thus by heating a mixture of acrylonitrile and a tertiary phosphine 2,4-dicyano-butene-1 is obtained (see French Patent Specification No. 1,366,- 081), which on hydrogenation yields Z-methyl-glutaronitrile.

It is also known that heating a mixture of acrylontrile, a tertiary phosphine and a proton donor such as water or an alcohol (see French Patent Specification No. 1,3 85,- 883) yields a mixture of monoethylenic dinitriles having 6 carbon atoms, which are straight-chain or branched. The amount of linear dimer is however always low. It is also known to dimerise acrylonitrile to 1,2-dicyano-cyclobutane, the hydrogenolysis of which yields adiponitrile, but this process requires high temperature and pressure conditions. It has been proposed to convert acrylonitrile directly into adiponitrile by hydrodimerisation processes using nascent hydrogen. Thus, according to U.S. Patent Specification No. 3,133,956 adiponitrile may be obtained by reacting acrylonitrile in aqueous solution with a finely divided dispersion of sodium in an inert organic solvent. The yields of adiponitrile are always low, relative to both the acrylonitrile and the metallic sodium consumed. Equally, treating acrylonitrile with magnesium in an aliphatic primary mono-alcohol in the presence of mercuric chloride as an activator (as described in U.S. Patent Specification No. 2,439,308) only gives low yields.

Various processes for the chemical dimerisation of esters of a,fi-ethylenic acids such as alkyl acrylates and methacrylates have also been proposed. In these processes, linear or branched products are obtained, as is the case with acrylonitrile. Thus alkyl Z-methylene-glutarates have been obtained (see U.S. Patent Specification No. 3,074,- 999) by bringing alkyl acrylates into contact with tertiary phosphines at between -10 and +100 C. in an inert solvent. In French Patent Specification No. 1,229,702 a process for the dimerisation of olefinic compounds has also been described which consists in heating the compounds in the presence of a noble metal derivative such as ruthenium chloride, working under the autogenous pressure of the reagents. Thus methyl acrylate yields methyl a-dihydromuconate by prolonged heating at 210 C. in the presence of ruthenium chloride and methanol.

Some of the process quoted above have been applied to mixtures of acrylonitrile with alkyl acrylates. In this case mixed coupling products are obtained as well as the dimerisation products of each of the monomers used. Generally speaking, the coupling behaviour of the two mono- 3,828,092 Patented Aug. 6, 1974 mers is the same as their behavior on dimerisation. Thus U.S. Patent Specification No. 3,225,082 describes coupling acrylonitrile with acrylates such as ethyl acrylate catalytically. For this purpose, a mixture of acrylonitrile and acrylate is heated at 50-190 C. under anhydrous conditions in the presence of a tertiary phosphine. As in the case of the processes of French Patent Specification No. 1,385,883 and U.S. Patent Specification No. 3,074,999, this process does not allow linear coupling products to be obtained. Besides the non-linear dimerisation products of acrylonitrile and the acrylate (2-methylene-glutaronitrile and alkyl Z-methyIene-glutarates), alkyl 2-methylene-4- cyano-butyrates are isolated.

It has now been found that a range of exclusively linear coupling products, as well as dimerisation products, can be obtained from acrylonitrile and alkyl esters of acrylic acid, without resorting to high temperatures, if a mixture of acrylonitrile and an alkyl acrylate is heated under hydrogen pressure in the presence of a ruthenium compound catalyst. The invention accordingly provides a process for the production of alkyl w-cyano-valerates and S-cyanopenten-4-oates which comprises heating a mixture of acrylonitrile and an alkyl acrylate under hydrogen pressure in the presence of a ruthenium compound as catalyst. During the reaction coupling products, in particularly alkyl 5-cyano-penten-4-oates and alkyl w-cyanovalerates, and dimerisation products of acrylonitrile and alkyl acrylates such as cis and trans 1,4-dicyano-butene-1 and alkyl a-dihyromuconates, as well as their hydrogenation products, namely adiponitrile and alkyl adipates, are simultaneously formed.

The relative proportions of these products depend on the operating conditions, namely duration of reaction, hydrogen pressure, temperature, maintenance of the pressure at a constant value or pressure drop during the reaction, nature and concentration of the catalyst, and acrylonitrile/acrylate ratio. All these parameters, which are discussed below, are interdependent and a judicious choice of them makes it possible to direct the reaction towards the preponderant formation of a given compound.

The catalysts which can be used in the new process are inorganic or organic derivatives of ruthenium such as the halides, thiocyanates, the salts of inorganic oxygen-containing acids such as the sulphates, nitrates, oxyhalides and hydroxyhalides, and the salts of organic aliphatic, cycloaliphatic or aromatic acids such as the acetate, oxalate, stearate and naphthenate. The alcoholates and the phenate may also be used. Other inorganic or organic ruthenium compounds which can be used include the alkali metal and alkaline earth metal ruthenates, the mixed salts of ruthenium and an alkali metal such as the sodium or potassium halogenoruthenates, and the halogenated and nitrosylated or aminated compounds such as nitrosochlororuthenium or trichlororuthenium hexamine. The chelates such as the acetylacetonates, optionally substituted by, for example, aliphatic or cycloaliphatic groups or by halogen atoms, such as 3-bromo-2,4-pentadionato-ruthenium(III) or 1,1,1 trifluoro 2,4 pentadionato-ruthenium(l1l), the glyoximates, quinolinates, salicylaldehydrates, and the derivatives of ethylene diamine, of a,a'-dipyridyl, and of o-phenanthroline are also suitable. Another especially suitable class of catalyst consists of the complexes which ruthenium derivatives form with electron donors. Such complexes are, for example, obtained by using halogenated, carbonylated or nitrosylated derivatives of ruthenium as the ruthenium derivatives and substances having pairs of lone electrons such as the phosphines, arsines, stibines, amines or substances capable of forming structures having pairs of lone electrons and thus also able to act as electron donors, as the electron donors. In particular the complexes formed with electron donors which are specifically cited in French Patent Specification No. 1,337,558 may be used.

Thus complexes produced by the reaction of ruthenium compounds, especially the halides and hydrohalides, with aliphatic or cycloaliphatic monoolefines and diolefines, such as for example, butadiene, isoprene, or cyclooctadiene, and with activated olefines, such as acrylic or methacrylic derivatives like acrolein, methacrolein or acrylamide, or with saturated or unsaturated aliphatic, cycloaliphatic or aromatic nitriles such as acetonitrile, propionitrile, acrylonitrile, methacrylonitrile, cyanocyclohexane, benzonitrile or toluonitrile, and with saturated or unsaturated dinitriles such as malouitrile, succinonitrile, adiponitrile, the dicyauobutanes, the dicyanocyclobutanes, the dicyanobutenes, and aliphatic or aromatic isonitriles are suitable. Such complexes may be prepared by heating a ruthenium halide with an electron donor, optionally in the presence of a solvent which may itself participate in the preparation of the complex.

To carry out the new process an amount of catalyst corresponding to an amount of metallic ruthenium of between 0.04 and 1.2% by weight of the mixture of acrylonitrile and alkyl acrylate which is to be treated is generally suitable. These lirnits are however not rigid and in the case of particularly active ruthenium derivatives, such as ruthenium trichloride or acetylacetonate, smaller amounts, e.g. 0.01% or even 0.001% of ruthenium, may be used. The catalysts may be used in the solid state, in a finely divided form, in suspension or in solution in the monomers, in water or in an organic solvent which is inert under the reaction conditions. The catalysts do not change, or

only change very slightly, during the reaction and may be re-used for a certain number of operations without it being necessary to regenerate them each time.

It is essential for the reaction to be carried out in the presence of hydrogen which can be introduced all at once, or in several stages, or even continuously to maintain a constant pressure of hydrogen. The pressure and temperature may vary within certain limits, most commonly from 1 to 50 bars and from 50 C. to 150 C. respectively. There is no advantage in working outside these limits. Below the lower values the reaction proceeds only slowly while above the upper values excessive amounts of propionitrile and alkyl propionates form, at the expense of the desired products, by direct hydrogenation of acrylonitrile and the acrylates. Similarly, increasing the duration of the reaction at a given hydrogen pressure increases the formation of saturated products. The most advantageous working conditions are generally within the range of to 40 bars pressure and 100 to 130 C.

The molar ratio acrylonitrile/acrylate is not critical, and may, for example, be from 1:3 to 3:1. The acrylonitrile and alkyl acrylate used in the reaction may be either commercial products or freshly distilled, and either unstabilised products or distilled products to which very small amounts of a stabiliser such as hydroquinone, pt-butyl-pyrocatechol, p-nitrosodimethylaniline or ammonia have been added. The alkyl acrylate will generally be one in which the alkyl group contains 1 to 4 carbon atoms, especially methyl acrylate. Generally speaking, the monomers are introduced all at once into a pressure-resistant apparatus, but it has been observed that introducing part of the monomers into the apparatus and then introducing the remainder progressively during the reaction increases the percentage of coupling products at the expense of the dimerisation products.

The reaction is preferably carried out in bulk or in the presence of a diluent which is liquid and inert under the working conditions. The reaction period will usually be from 2 to hours.

When the reaction is ended, the unconverted monomers, the solvent (if any) and the hydrogenation products of the monomers, which are the sole volatile by-products formed, may be isolated by distilling the reaction mixture. The coupling products and the dimerisation products and their hydrogenation derivatives are then separated by fractional distillation. All the products are of similar industrial value: the alkyl 5-cyano-penten-4-oates and w-cyanovalerates may be converted, by hydrogenation, into alkyl w-aminocaproates which are intermediates for the preparation of polycaprolactam; the dicyanobutenes may 'be converted by hydrogenation into adiponitrile which is a starting material for the preparation of hexamethylene diamine used in the synthesis of polyamides; and the alkyl a-dihydromuconates may be hydrogenated to alkyl adipates, which may be saponified to yield adipic acid or used directly in the synthesis of polyesters by reaction with glycols.

The following examples illustrate the invention. The pressures quoted are relative pressures.

EXAMPLE 1 0.1 g. of ruthenium chloride (0.48 millimol), 32 g. of acrylonitrile (0.605 mol), 38.4 g. of methyl acrylate (0.440 mol), and 0.05 g. of hydroquinone are introduced into a 250 cm. stainless steel autoclave fitted with a vibratory stirrer system. The autoclave is purged with hydrogen and a hydrogen pressure of 40 bars is then set up. The contents of the autoclave are kept at 110 C. for 5 hours, with stirring. The pressure rises to 48 bars and is then kept at 40 bars by periodically introducing hydrogen. The reaction mixture is then cooled to ambient temperature. The total hydrogen pressure drop is 58 bars. The apparatus is degassed and the reaction mixture is distilled in vacuo. A volatile fraction containing methyl propionate, propionitrile, acrylonitrile (1 g. determined by vapour phase chromatography) and methyl acrylate (20 g.) is first obtained, followed by 18.3 g. of a less volatile fraction distililng at between 60 and 110 C. in a vacuum of 0.6 mm. Hg. The residue weighs 1.5 g.

Vapour phase chromatography shows the less volatile fraction to contain: methyl adipate (0.2 g.), methyl oz-dihydromuconate (l g.), cis and trans 1,4-dicyano-butene-l (9.6 g.), cis methyl 5-cyanopenten-4-oate (2.5 g.) trans methyl 5-cyano-penten-4-oate (3.2 g.), methyl w-cyanovalerate (0.5 g.), and adiponitrile (1.3 g.). This corresponds to 6.5% of dimerisation and hydrodimerisation products of methyl acrylate, 59.5% of dimerisation and hydrodimerisation products of acrylonitrile, and 34% of coupling products.

The cis and trans methyl 5-cyano-penten-4-oates are isolated by fractional distillation. They are characterised by microanalysis and by their infra-red and nuclear magnetic resonance spectra. They have the following properties: cis isomer, b.p.=89-91 C./4 mm. Hg., n =1,4482; trans isomer, b.p. =107 C./3 mm. Hg, n =l.4550.

EXAMPLE 2 0.2 g. of ruthenium chloride (0.96 millimol), 16 g. of acrylonitrile (0.302 mol), 57.6 g. of methyl acrylate (0.670 mol), and 0.05 g. of hydroquinone are introduced into a 250 cm. autoclave. Working as in Example 1, a hydrogen pressure of 40 bars is then set up and the contents of the autoclave are heated to 110 C. The pressure is maintained at 40 bars Whilst hydrogen is introduced as in Example 1. These conditions are maintained for 5 hours. After cooling the reaction mixture, it is found that the total pressure drop is 60 bars. By distilling the reaction mixture a more volatile fraction containing 9.5 g. of methyl acrylate (0.11 mol) is first isolated, followed by 14.7 g. of a less volatile fraction boiling at between 60 and C./0.4 mm. Hg. Analysis of the latter fraction by vapour phase chromatography shows it to contain:

EXAMPLE 3 Example 2 is repeated using 24 g. of acrylonitrile (0.454 mol) in place of 16 g. (0.302 mol). The total pressure drop is 97 bars. Distilling the reaction mixture gives first a more volatile fraction containing 11 g. of methyl acrylate by vapour phase chromatography but no acrylonitrile, followed by 22 g. of a less volatile fraction comprising the following.

EXAMPLE 4 0.2 g. of ruthenium chloride (0.96 millimol), 19.7 g. of acrylonitrile (0.372 mol), 23.7 g. of methyl acrylate (0.276 mol), and 0.05 g. of hydroquinone are introduced into a 125 cm. autoclave connected to a source of hydrogen through a pressure-reducing manometer. The autoclave is purged with hydrogen. Hydrogen is then introduced and a constant pressure of bars is maintained at 110 C. for 6 hours whilst hydrogen is continuously introduced through the manometer. 9.25 litres of hydrogen are introduced in this way. At the end of the reaction the autoclave is brought to ambient temperature and degassed. The reaction mass is worked up as in the preceding example. 23.25 g. of a fraction which contains neither acrylonitrile nor methyl acrylate are first obtained, followed by 16.20 g. of a fraction the composition of which is as follows:

Weight, Content,

percent Product Methyl 5-cyano-penten-4-oate:

(is 0 Trans EXAMPLE 5 0.2 g. of ruthenium acetylacetonate (0.5 millimol), 16 g. of acrylonitrile (0.302 mol), 38.4 g. of methyl acrylate (0.440 mol), and 0.1 g. of hydroquinone are introduced into the autoclave used in Example 4. A hydrogen pressure of bars is set up and the contents of the autoclave are heated to 130 C. The pressure is restored to 40 bars by periodically adding hydrogen. The mixture is kept under these conditions for 7 hours and the autoclave is then cooled and degassed. The amount of hydrogen absorbed corresponds to a pressure drop of 169 bars. The reaction mass is worked up as in the preceding examples. A more volatile fraction which contains neither acrylonitrile nor methyl acrylate is collected, followed by 20.4 g. of a less volatile fraction the composition of which is as follows:

Methyl w-cyanovalerate.

6 EXAMPLE 6 0.4 g. of ruthenium acetylacetonate (1 millimol), 47.9 g. of methyl acrylate (0.560 mol), 40.1 g. of acrylonitrile (0.756 mol), and 0.1 g. of hydroquinone are introduced into a 250 cm. stainless steel autoclave connected to a source of hydrogen through a pressure-reducing manometer. The autoclave is purged with hydrogen and hydrogen is then introduced to a pressure of 7 bars. The contents of the autoclave are heated to C., and the pressure rises to 10 bars. These conditions are maintained for 6 hours whilst hydrogen is introduced throughout the operation to keep the pressure at 10 bars. At the end of the operation the autoclave is cooled. The amount of hydrogen consumed is 4.5 l. The reaction mass is worked up as in the preceding examples. 63.3 g. of a more volatile fraction are collected, which is shown by gas chromatography to contain 7.6 g. of acrylonitrile and 33.5 g. of methyl acrylate. 20.8 g. of a less volatile fraction and 1.9 g. of residue are thereafter isolated. Gas chromatography shows the less volatile fraction to have the following composition.

Weight, Content,

Methyl 5-eyano-penten-4-oate:

EXAMPLE 7 0.4 g. of ruthenium acetylacetonate (1 millimol), 48.5

- g. of methyl acrylate (0.565 mol), 39.6 g. of acrylonitrile (0.746 mol), and 0.1 g. of hydroquinone are heated at 110 C. in the apparatus used in Example 6 for 16 hours under a constant pressure of 10 bars of hydrogen. The reaction mass is worked up as in the preceding examples.

38.75 g. of a more volatile fraction consisting of propionitrile and methyl propionate are obtained followed by 44.6 g. of a less volatile fraction found chromato graphically to contain 15.6 g. of methyl adipate (35%), 15.6 g. of adiponitrile (35%), and 13.4 g. of methyl w-cyanovalerate (30%).

When the same experiment is repeated under a constant pressure of 5 bars of hydrogen, 36.9 g. of a more volatile fraction containing 10.5 g. of methyl acrylate are obtained, followed by 40.7 g. of a less volatile fraction the composition of which is as follows:

Weight, Content 7 EXAMPLE 8 0.4 g. of ruthenium acetylacetonate (1 millimol), 16 g. of acrylonitrile (0.302 mol), 19 g. of methyl acrylate (0.220 mol), 0.04 g. of hydroquinone, and 60 cm. of Z-methoxy-ethanol are introduced into the 250 cm? autoclave used in the preceding examples, and the contents of the autoclave are then kept at 110 C. for 6 hours at a constant hydrogen pressure in the preceding examples 8 EXAMPLES 10 TO 12 A series of experiments is carried out by introducing 16.7 g. of acrylonitrile (0.315 mol),- 27 g. of'meth yl acrylate (0.315 mol), 0.05 g. of hydroquinone, and varying amounts of dichloro-tetrakis acrylonitrile' ruthenium into a 125 cm. stainless steel autoclave. The reaction is carried out at 110 C. at a constant hydrogen pressure under the conditions specified in the following table:

Weight i Composition of dimers, percent Catalyst in H Dura- More volpressure tion, atile frac- Dimer-s Acrylate Coupling Aerylonitrile Example Grams Mmols 1n bars hours tion in g. in g. dimers products dimers and 75.4 g. of a more volatile fraction which contains EXAMPLE 13 neither acrylonitrile nor methyl acrylate and 15.4 g. of a less volatile fraction are obtained. The latter is found to contain:

Weight, Content Product g. percent Methyl adipate 1. 7 26 5 Methyl a-dihydromuconate 2. 4 Adipnnifriln 7 4.5, 3 Methyl u-cyanovalerate 4. 3 28. 2

The experiment is repeated with only 0.1 g. of ruthenium acetylacetonate. 13.1 g. of a less volatile fraction are isolated containing:

Weight, Content,

Product g. percent Methyl adipate 0. 1 z 6 Methyl a-dihydromuconate 0. 7 Adipnnii'riln 5.3 75 Cis and trans 1,4-dicyano-butene-1 4. 5 gefilfiyl greyanovalezateiue 1 e y -c anoenen -oae:

on y p o. 4 19 Trans- 1.1

EXAMPLE 9 Weight, Product g.

Methyl adipate 1 Content percent Methyl u-dihydromuconaten Cis and trans 1,4-dicyanobutene-1. Adiponitrile The dichloro-tetrakisacrylonitrile ruthenium-II used as the catalyst is prepared by heating 64 g. of acrylonitrile (containing 0.08 g. of hydroquinone) with 4 g. of ruthenium trichloride dissolved in 80 cm. of Z-methoxy-ethanol under reflux for 28 hours, and then filtering the unreacted ruthenium chloride and concentrating the filtrate in vacuo.

1.6 g. of ruthenium acetylacetonate (4 mmols), 13.2 g. of acrylonitrile (0.25 mol), and 21.5 g. of methyl acrylate (0.25 mol) are introduced into a 750 cm. autoclave. The contents of the autoclave are heated to C. under a hydrogen pressure of 10 bars and maintained under these conditions for 3 hours. 144 cm. of an equimolecular mixture of acrylonitrile and methyl acrylate are then injected over the course of 5 hours under the same pressure and temperature conditions. In total, 48.8 g. of acrylonitrile (0.92 mol) and 78.7 g. of methyl acrylate (0.92 mol) are injected. On distilling the reaction mass, 78.4 g. of a more volatile fraction containing 4 g. of methyl acrylate and no acrylonitrile is obtained, followed by 69.5 g. of a less volatile fraction found to contain:

Weight, Content,

We claim: 1. A process for the production of alkyl w-cyano- Nalerates and 5-cyano-penten-4-oates in which the said alkyl is of 1 to 4 carbon atoms, which comprises:

heating at 50 C. to C.,

a mixture of acrylonitrile and an alkyl acrylate in which the said alkyl is of l to 4 carbon atoms,

under a hydrogen pressure of 1 to 50 bars in the presence of a ruthenium compound as catalyst.

2. The process of claim 1 in which the amount of catalyst is 0.04% to 1.2% by weight of the mixture of acrylonitrile and alkyl acrylate.

3. The process of claim 1 in which the catalyst is ruthenium trihalide, ruthenium acetylacetonate, or dihalotetrakis(acrylonitrile)ruthenium.

4. The process of claim 1 in which the catalyst is ruthenium chloride, ruthenium acetate, ruthenium oxalate, ruthenium stearate, ruthenium acetylacetonate, 3-bromo- 2,4-pentadionatoruthenium (HI), 1,l,1-trifluoro-2,4-pentadionatoruthenium(1H), ruthenium glyoximate, ruthenium quinolinate, ruthenium salicyaldehydate, a chelate of ruthenium with ethylene diamine, a,a -dipyridyl, or 0-phenanthroline, or a complex of ruthenium chloride with butadiene, isoprene, cyclooctadiene, acrolein, methacrm lein, acrylamide, acetonitrile, propionitrile, acrylonitrile, methacrylonitrile, cyanocyclohexane, benzonitrile, toluo nitrile, malonitrile, succinonitrile, adiponitrile, dicyanobutane, dicyanocyclobutane, or dicyanobutene.

1,155,439 860,321 References Crted 1,451,443 UNITED STATES PATENTS 5 1,472,033 10/1961 Minisci et a1. 2'60-465.4 1,411,003

8/ 1964 Chiusoli 260-4654 12/1965 McClure 260--465.4

6/1972 Chabardes et a1. 2'60465.8 D 10 6/1969 Chabardes et al. 260465.8 X 12/1969 Cornforth et a1. 260-465.8

FOREIGN PATENTS JOSEPH PAUL. BRUST, Primary Examiner US. Cl. X.R. 

